The present invention relates generally to networks for communication of data and voice information. More particularly, the present invention relates to a dispatch call server and its use in a packet based communication network.
Dispatch communication networks including dispatch radio systems have been developed to provide two way and group calling in a radio system. Dispatch communication systems have several identifying characteristics. First, they provide talking on demand. A user who wants to communicate to another user activates a radio and begins speaking. This concept is broadly known as push to talk (PTT). Second, a dispatch communication network provides for group calling. A user can have a two-way conversation with another user or can select a group of users for a multi-party conversation. Third, dispatch radio links are one-way (also referred to as simplex or half duplex) in nature. A user cannot talk and listen at the same time. A channel is seized by the user's radio when a PTT button on the radio is pressed and while the user is talking. The channel is then released by the radio when talking stops or when the PTT button is released. Dispatch radio networks have been developed using both analog and digital radio technologies.
Generally, dispatch networks typically include a central controller which manages the various radio links in the system. The controller assigns channels and arbitrates between callers in the system. That is, in a two-way call, only one speaker can talk at a time because a dispatch network is limited to one-way communication. Also, in a group call, only one speaker can talk at a time so listeners don't hear two talkers at the same time. The controller operation is typically optimized to minimize response time, so that conversations in the network can progress with minimal delay or interference, even during heavy demand on the network.
In wireline or wireless systems, it is known to use packet based data networks to provide voice services. Various voice over internet protocol (VoIP) techniques have been developed for voice communication in such a network. An internet protocol session is set up between the communicating parties and voice packets are exchanged.
The Internet Protocol (IP) is designed for use in interconnected systems of packet-switched computer communication networks. The internet protocol provides for transmitting blocks of data called datagrams from sources to destinations, where sources and destinations are hosts identified by fixed length addresses. The internet protocol also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through “small packet” networks.
The internet protocol implements two basic functions, addressing and fragmentation. The internet elements use the addresses carried in the IP header to transmit internet datagrams toward their destinations. The selection of a path for transmission is called routing. The internet routers use fields in the internet header to fragment and reassemble internet datagrams when necessary for transmission through “small packet” networks.
It is desirable to adapt dispatch communication technology to IP and other packet switched network technology to enhance the flexibility of dispatch technology. Dispatch systems have a central controller to perform arbitration between multiple talkers. That is, the talking party of the group must complete his transmission before another group member can join in. However, in an uncoordinated, distributed network used for IP data, there is no way to arbitrate between contending transmissions.
Accordingly, there is a need for a method and apparatus for coordinating dispatch calls in a packet based network.